Machinery such as diesel engines and their fuel systems have numerous components to be assembled with important locational requirements. Some engines have electronically controlled fuel injection systems that include a solenoid valve threadably secured in a cartridge cavity of a body.
Such a valve is for controlling fuel flow between two lines of respective high and low pressure with diesel fuel pulses at pressures extending to high levels such as about 20,000 pounds per square inch. Sealing of the valve in the cartridge cavity is important to maintain the required pressure difference. When such a valve is closed, high pressure fluid will seek any available avenue of escape circumventing the blocked flow path through the valve, including between the valve and the cavity wall. Characteristically, the cartridge cavity has a high pressure port in its bottom surface and a low pressure port in its longitudinal surface which is generally cylindrical. Fluid communication between those ports should occur only through the valve.
The practice has been to process a metal (e.g., alloy steel), forged, body for housing such a valve in a sequence of steps including: machining, by milling, internal threads on the cavity wall for securing the valve while the body is in its soft condition before heat treatment; heat treating the body, with the threads, to a desired degree of hardness; and, after the heat treatment, machining a precise seal face at the bottom of the cavity. The valve is to be placed in position with the high and low pressure ports of the cavity communicating with ports in the valve itself. Then, external threads on the valve are secured to the internal threads of the cartridge cavity. The valve has a surface for fitting against the seal face of the cavity, normally with a metal seal gasket therebetween. However if the valve is tilted in the cartridge cavity, even by a few degrees, adequate sealing can be lost. Placing, and maintaining, the valve with its center line in precise perpendicular position in relation to the seal face in the cavity is what is intended.
When threads are milled in steel before heat treatment, they can be formed quickly, economically and accurately by standard milling equipment. Subsequent heat treatment can, however, deform the threads to an extent that the alignment of the solenoid valve is thrown off of perpendicularity. Grinding or polishing the previously milled threads, after the heat treatment, may be needed to provide adequately aligned threads. On close inspection, the surfaces of the threads will show heat treat residue or scale and metal to metal galling.